Self-Assembling Functionalized Amino Acids into Unusual Shapes
- PDF / 267,922 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 25 Downloads / 131 Views
Self-Assembling Functionalized Amino Acids into Unusual Shapes Justin R. Barone, Naresh K. Budhavaram, and Katherine J. Harvey Biological Systems Engineering Dept., Virginia Tech, 303 Seitz Hall (0303), Blacksburg, VA 24061, U.S.A. ABSTRACT Multi-component small molecule systems that are amphiphilic or that can hydrogen bond end-toend or side-to-side have been shown to self-assemble into a variety of shapes including fibers, rods, sheets, plates, spheres, and tubes. Recently, we have identified a simple route to selfassemble the same shapes from one-component systems. The structures form by attaching ethyl vinyl sulfone (EVS) to amino acids in water at room temperature. Choice of amino acid, amount of EVS substitution, and solvent conditions determine the final shape. Functionalized amino acids spontaneously form structures like fibers, spheres, tubes, and donuts when dried from solution. Here we focus on fibers and tubes. INTRODUCTION Self-assembly is an interesting processing concept because it relies on minimizing the free energy of interaction embodied in the molecules to create structures rather than the application of external energy. Nature does this by very precisely forming molecules that will spontaneously interact in aqueous solution and presumably is its way to conserve energy. Self-assembly proceeds from the molecular level by first constructing an elementary building block. For example, prions are composed of elementary nanometer-sized β-sheets.1 In nature, the β-sheet is a fairly common protein building block. A typical β-sheet forms when two peptide molecules form a β-strand through amine-carbonyl hydrogen bonding on the peptide main chain. Selfassembly continues by many β-strands forming a β-sheet and then the sheets stack into larger structures until a nanometer to micrometer sized object results such as a fiber.2 β-structures in general perform a variety of functions in nature including bearing load, stabilizing enzymes, protecting bacteria, and acting as recognition motifs for enzymes.3, 4 Recently, it has been shown that molecules other than the carbonyl can form β-structures. Sulfonyls have been used in βstrand mimics for therapeutics.5, 6 Essentially, the sulfonyl replaces the carbonyl in a β-strand hydrogen bond. One origin of many common diseases is protease cleavage of proteins required for biochemical function. The protease attacks the protein rendering it unable to do its job and initiating disease. A lot of these protease enzymes are known to bind to a β-strand motif. Therefore, β-strand mimics introduced into the body could act as enzyme inhibitors by forming similar structures recognized by the enzyme but not be made of natural protein. Two important structures self-assembled in nature are micron-sized fibers and tubes. The fiber is the material of choice in nature for structural applications. Micron-sized fibers of (a) silk capture insects, (b) keratin provide protection and support to animals, and (c) collagen impart rigidity to cartilage.4 Tubes are a common structure in nature, for
Data Loading...
